1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly to a method and apparatus for performing effective feedback in a wireless communication system supporting multiple antennas.
2. Discussion of the Related Art
Generally, Multiple-Input Multiple-Output (MIMO) technology will hereinafter be described in detail. In brief, MIMO is an abbreviation for Multi-Input Multi-Output. MIMO technology uses multiple transmission (Tx) antennas and multiple reception (Rx) antennas to improve the efficiency of transmission/reception (Tx/Rx) data, whereas the conventional art generally uses a single transmission (Tx) antenna and a single reception (Rx) antenna. In other words, MIMO technology allows a transmitting end and a receiving end to use multiple antennas so as to increase capacity or improve performance. If necessary, the MIMO technology may also be called multi-antenna technology. In order to correctly perform multi-antenna transmission, the MIMO system has to receive feedback information regarding channels from a receiving end designed to receive multi-antenna channels. Various feedback information fed back from the receiving end to the transmitting end in the legacy MIMO wireless communication system may be defined, for example, a rank indicator (RI), a precoding matrix index (PMI), channel quality information (CQI), etc. Such feedback information may be configured as information appropriate for the legacy MIMO transmission.                There is a need for the new system including the extended antenna configuration as compared to the legacy MIMO wireless communication system to be developed and introduced to the market. For example, although the legacy system can support a maximum of 4 transmission antennas, the new system having the extended antenna configuration supports MIMO transmission based on 8 transmission antennas, resulting in increased system capacity.        